In petroleum well drilling operations, as well as other types of wells, a hole is bored into the earth, typically by a drill bit. Drilling mud is generally circulated in and out of the well to carry away the debris from the hole being drilled. The debris, such as rock, shell etc., being returned to the surface for removal is called drill cuttings. Although the drilling fluids, or mud as it is called, also perform other tasks, due to their complex formulation, the mud is still a contaminant to the environment. Once the contaminated (mud-coated) drill cuttings and drilling fluids are circulated out of the well, the contaminated fluid and drill cuttings are pumped or otherwise conveyed to a shale shaker (many commercial types are available and well known to those skilled within the art), whereby the contaminant fluid and drill cuttings pass over a screen on the shale shakers and other fluid cleaning equipment, thus separating substantially all of the drilling fluid from the drill cuttings. However, the residual fluid left on the drill cuttings separated from the drilling fluid is still a contaminant to the environment and must be handled in an environmentally safe way. The prior art teaches and discloses a great many methods and apparatus for handling, conveying, transporting, cleaning, drying, grinding, and injecting the contaminated drill cuttings and residual fluids. Many industries completely unrelated to the petroleum drilling industry utilize vacuum hoppers, mechanical discharge hoppers and cuttings boxes for accumulating and transporting cuttings materials. Often such systems are bulky and require a great deal of storage space. In locations such as off shore drilling platforms such storage space is always scarce.
Cuttings grinding and disposal systems taught by the prior art, although much improved over the years, still require a significant complication of valves, manifolds, shakers, pumps, adjustable jets, etc., and several skid modules such as conveying and holding and circulating system skids, as well as a separate injection pump skid. The resulting systems perform very well in many cases, but require a good many highly trained operators to set up, operate, and maintain, have high operating costs, and use considerably more deck space than is now believed to be necessary.
These systems require constant monitoring and/or the use of highly complicated computer automation requiring highly trained technicians. The older, less complicated cuttings grinding and disposal systems were unable to handle the volume of large bore holes and their process rates. These older systems often lacked the secondary shale shakers, manifolds, and adjustable jets necessary to minimize the shut down times needed for cleaning out the unground cuttings from the grinding pumps. Further, manifolds/valves wore out or plugged quickly.
Poor visibility of the cuttings transfer decontamination process hampers the ability of the operator to control the various operations in time to prevent costly shutdowns. The prior art for the most part felt that it was best to completely seal the top of the grinding unit and vacuum the cuttings into the grinding tank with fluid already in it. While at first this seems like a good solution, the problem that results is that the operator cannot see the slurry that is created by grinding the cuttings in fluid. As described above, without being able to see the slurry thickening occurs and the operator is unable to determine how much fluid is required to maintain a proper mixture. Others have solved this problem by adding a second grinding tank with an open top merely for grinding the cuttings. Therefore, the primary, completely covered grinding tank becomes a transfer tank and the second tank becomes an unnecessary added grinding tank within the system. The ability to vacuum cuttings from several cuttings troughs requires several grinding transfer tanks. These tanks are cumbersome, require extra personnel to operate, take up space on the drilling rig which is hard to find, since drilling rigs have a limited amount of space available, and the operators still cannot see the conditions in these tanks which cause an operational nightmare to the operators and the drilling rig.
In reviewing the prior art developed to date if becomes clear that improvements are needed to overcome the disadvantages discussed above. For example, there needs to be a way to deliver the cuttings, unobstructed and at any volume, from the collection trough, via gravity or a continuous open discharge vacuum hopper that further allows gravity feeding of the cuttings thru a cuttings dryer to remove any residual drilling fluid or contaminates or gravity feed the cuttings directly into the grinding tank fluid. A more simplified transfer system is needed whereby there are no manifolds to complicate or wear out and no shale shakers to complicate or create unsafe and unclean working conditions.
The size of the grinding and holding tanks needs to be reduced or eliminated, thus allowing smaller skids to fit in the available space. The simplified cuttings grinding and disposal system should also use less electricity and provide a significant reduction in component parts and valves that complicate the system and tend to wear quickly. Such systems should require significantly less personnel to operate and be much simpler to automate. It is believed that it is now possible to provide a cuttings grinding and disposal system capable of being operated without stand-alone crews, instead utilizing personnel already aboard the rig who can provide limited amounts of time to the cuttings grinding and disposal systems.